What are .SDK files?

.SDK files are saved Sudoku puzzles in SadMan Sudoku format. They can be created and opened by
SadMan Sudoku and also some other Sudoku applications.

The files are in a simple text file format, which means that if you simply want to see the puzzle, you
can even open them using Windows Notepad.

The file may simply consist of 81 characters in a 9 x 9 array, or there may be up to five sections of data
giving header information, the initial puzzle, the current state of a partially solved puzzle, any
pencil marks, and any cell colours.

The various header fields are identified by a # followed by a single character: